1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing a semiconductor device, and in particular, to a technique to stack substrates each having an integrated circuit chip.
2. Description of the Related Art
In recent years, stacked semiconductor devices have been proposed in each of which a plurality of integrated circuit chips (LSI chips) are stacked on one another.
FIG. 10 is a diagram showing a method of producing such a stacked semiconductor device. This method connects substrates 10 together on each of which an LSI chip is mounted (such substrates will hereinafter be referred to as chip mounted substrates), via a substrate 20 on which no chips are mounted (such a substrate will hereinafter be referred to as a chip-less substrate). Usually, more chip mounted substrates 10 and chip-less substrates 20 are stacked. For simplification of description, the figure shows only a part in which the two chip mounted substrates 10 and the one chip-less substrate 20 are stacked on one another.
An LSI chip 12 is mounted on a substrate main body 11 of the chip mounted substrate 10. External terminals (not shown) of the LSI chip 12 are connected to respective interconnects (not shown) provided on the substrate main body 11 via anisotropic conductive materials 14. The interconnects are connected to respective lands 16 provided on the substrate main body 11. The lands 16 are connected to respective through plugs (via plugs) 17 penetrating the substrate main body 11.
A plurality of the chip mounted substrates 10 are mounted on the chip-less substrate 20. Openings (device holes 22) are each formed in the chip-less substrate 20 in association with an area of the chip mounted substrate 10 in which the LSI chip 12 is mounted. Furthermore, a substrate main body 21 of the chip-less substrate 20 is formed with lands 23 and through plugs (via plugs 24) penetrating the substrate main body 21.
When the chip mounted substrates 10 and the chip-less substrate 20 are stacked on one another, the chip mounted substrates 10 and the chip-less substrate 20 are bonded together using a resin-based adhesive 29 applied to front and back surfaces of the chip-less substrate 20.
In this manner, in the above described conventional semiconductor device, the chip mounted substrates 10 and the chip-less substrate 20 are bonded together using the resin-based adhesive 29. However, the resin-based adhesive 29 does not have a high adhesive strength. Accordingly, a bonded area must be enlarged in order to obtain a sufficient adhesive strength. Disadvantageously, this unavoidably increases the area of each chip mounted substrate 10, preventing an increase in the number of chip mounted substrates 10 that can be mounted on the one chip-less substrate 20.
Furthermore, if the resin-based adhesive 29 is applied after the formation of the device hole 22, the device hole 22 may be filled with the adhesive 29 and other problems may occur. Thus, the adhesive 29 is applied to both surfaces of the substrate main body 21 of the chip-less substrate 20 before the formation of the device holes 22. However, since the adhesive 29 is applied to both surfaces of the substrate main body 21, production efficiency may disadvantageously be degraded. Furthermore, when the device holes 22 are formed, the adhesive 29 may form flashes or the like. This may degrade reliability.
As described above, in the prior art, the chip mounted substrates and the chip-less substrate are bonded together using the resin-based adhesive, which does not have a strong adhesive force. Thus disadvantageously, it is difficult to reduce the size of each chip mounted substrate, and the number of chip mounted substrates that can be mounted on the chip-less substrate cannot be increased. Furthermore, in the prior art, since the adhesive is applied to both surfaces of the chip-less substrate before the formation of the device holes, the production efficiency and reliability may disadvantageously be degraded.